Sampling tubes injection molded from thermoplastic synthetic resin material have been provided in the past as cylindrical vessels, open at opposite ends and provided with an intermediate bottom or well in which the sample is retained and which serves to allow even a small specimen to have sufficient depth to enable its removal by the pipette or needle.
A tube of this type, for example for use with conventional laboratory instruments, can be received in a rack provided with cavities dimensioned to receive the sampling tubes and can have a diameter of say 12 mm and a length of 75 mm.
Because of the recessed configuration of the intermediate bottom, the sampled material, e.g. blood, urine or serum, can be of sufficient depth to enable removal of the sample or part of the sample and the open end of the tube insures easy accessibility to the sample. Since the needle or pipette tip for extraction the sample does not have to reach to the end of the tube but merely into the well, usually conical, provided in the intermediate bottom or partition, there is little danger of damage to the needle.
The entire tube is usually produced by an injection molding process in one piece from the thermoplastic synthetic resin and circularly cylindrical walls extend upwardly from the well to form the mouth of the vessel and downwardly from the well to provide a bottom which can rest on a horizontal surface or on a support in the rack. The tube can be produced by injection molding in one piece through the use of two cores which define the hollow spaces of the tube above and below the well-forming intermediate bottom.
A problem with the method of manufacture used to date has been that the use of two cores, which must be withdrawn in opposite directions from the tube, has limited the configuration of the sample tube to one in which the walls extend vertically in both directions from the bottom or well.
This can be a drawback when the receptacle in which the tube is to be received has a hemispherical or curvilinearly concave surface on which the tube is to stand. Racks, stands or holders of this shape cannot stably receive the cylindrical bottom wall of a sampling tube of the type described fabricated with two cores.
One solution to this problem, of course, is to initially provide a sampling tube with a rounded bottom in which the sampled material is to be received, but this solution does not have the advantages of an intermediate bottom or well located above the lower end of the tube as described above. Another possibility, of course, is to assemble the sampling tube of two pieces, one of which forms the lower part and is rounded. This system has the disadvantage that it requires additional assembly steps and increases the fabrication costs, which may be substantial especially when the tubes are to be mass produced.
Other systems may utilize hangers or lips of the sampling tube which suspend the sampling tube in the rack or otherwise solve the problem of stability by retaining the sampling tube in other ways on the holders.
None of these approaches, however, has proved to be satisfactory.